I. Field of the Invention
The present invention relates to a valve for the venting circuit of a liquid tank, in particular a fuel tank with which a motor vehicle may be equipped.
II. Description of Related Art
Liquid tanks, in particular fuel tanks for motor vehicles, are nowadays generally provided inter alia with a venting circuit. This circuit allows air to be introduced into the tank in the event of underpressure (especially for compensating for the volume of liquid consumed) or allows the gases contained in the tank to be removed in the event of overpressure (especially in the event of overheating). This circuit also allows the channeling and possible filtering of the gases that have to be discharged into the atmosphere, for the purpose of meeting the ever stricter environmental requirements in this regard.
The venting circuit includes, in a known manner, at least one valve that prevents, as far as possible, liquid being expelled from the tank when the tank is turned upside down or at an excessively high angle of inclination. This venting valve must provide a rapid and reliable response when these conditions arise, but with minimal sensitivity to transient phenomena such as in particular very high flow rates, overpressure in the tank or low-amplitude waves. It must also ensure that there is minimal liquid carried over into the canister (or the chamber containing a substance, usually active carbon, which adsorbs the fuel vapors) in normal operation and during filling, for fear of saturating said canister and making the decontamination of the gases discharged into the atmosphere ineffective. This phenomenon is generally called LCO (liquid carry over) in the jargon of the yield.
Many venting valves employ a float having an upper needle or tip which closes off an aperture for connecting the tank to the venting circuit. One way of reducing the risk of LCO with this type of valve is that described in application US 2002/0124909, which consists in surrounding the shaft of the valve with a baffle and providing the shaft and the valve with apertures arranged so as to force the gas to be vented into a tortuous passage allowing it to be purified of the liquid.
One drawback of this type of system is its bulkiness (total diameter of the shaft/baffle assembly). One way of solving this problem could consist in providing the valve with an internal baffle, but this would then reduce the volume available for the float to slide in, which therefore becomes “thinner”, hence a larger dispersion on the liquid line and poorer reproducibility in terms of performance of the valve.
Furthermore, when the float rests in the high position (closed venting aperture) for a long time, fuel can accumulate around the aperture, on the plane surfaces present in this region (especially on the head of the float). As venting is then impossible, the pressure rises in the tank. Consequently, when the valve reopens, the instantaneous speeds are very high, hence a substantial risk of fuel droplets being carried over.